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More Troublesome Water Weeds
Targeted by Researchers

Close-up of yellow starthistle (Centaurea
solstitialis).(K9658-1)

A pleasant saltwater lagoon
on the sunny coast of southern California made botanical history last year when
a dreaded marine alga, Caulerpa taxifolia, showed up there. The
infestation at Agua Hedionda lagoon in Carlsbad, about 30 miles north of San
Diego, was the first discovery in the Western Hemisphere of the Mediterranean
strain of this notorious alga.

Caulerpa was next detected in Huntington
Harbor, a small, isolated marina near Long Beach, California.

ARS plant
physiologist Lars W. J. Anderson, together with industry, university, state,
and federal colleagues, worked quickly to quash the weed before it could spread
farther up the coast.

In preliminary experiments, Anderson and co-researchers
tried several commonly used aquatic herbicides but found that liquid chlorine,
injected under 10- to 20-foot-square black plastic tarpaulins spread atop the
weed, worked best at Agua Hedionda. At Huntington Harbor, they used solid,
puck-shaped disks of chlorine instead of liquid. Both killed the algae.
"Nothing else seemed to work," Anderson says. He is with the ARS Exotic and
Invasive Weeds Research Unit, stationed at Davis, California.

Sometimes referred to as "killer algae," C.
taxifolia flourishes in warm saltwater harbors, bays, and lagoons. It
spreads remarkably fast, crowding out native species of algae and sea grasses.
"Caulerpa essentially ruins conditions for a whole host of marine
animals, such as small mollusks," says Anderson.

"No one knows exactly how it ended up at the lagoon or at
Huntington Harbor," he says, "but we suspect that someone dumped the contents
of an aquarium." Caulerpa was listed by the federal government as a
noxious weed in 1999, which means that it is illegal to sell it in the United
States. However, there is still a market for it. People like to have this weed
in their fish tanks because it grows so well. They may not even be aware of the
effects it can have if it escapes to the outdoors.

Today, the black plastic tarps still remain in place. The
scientists and their collaborators continue to monitor the outbreaks regularly.
"We know that chlorine kills the top of the Caulerpa plants," Anderson
explains, "but the real question is what's happening below, in the mud. We know
that the plant forms structures called rhizoids that could produce new growth.
We need to be sure that the chlorine kills them."

In testing the viability of the rhizoids after aboveground
parts of the plant have been killed, Anderson is collaborating with Susan
Williams, director of the University of California at Davis Bodega Marine
Laboratory, just north of San Francisco. "We're also looking at other
algicides," notes Anderson.

Unlike the algal newcomer Caulerpa, a bamboolike
invader called giant reed or giant cane has been an unwanted intruder in
California for at least 100 years. Known to scientists as Arundo donax,
this member of the grass family can grow 3 to 7 inches a day, reaching 30 feet
in height. Plants sport feathery white plumes called panicles.

Arundo is used as an ornamental plant for
landscaping and as a source of reeds for musical instruments, such as bassoons
and bagpipes. Its cellulose can be used for papermaking.

Found from Maryland to California, Arundo thrives
along streams and ditches. A fierce invader of freshwater ecosystems,
Arundo crowds out riparian regulars like alders, cottonwoods, and
willows that would otherwise provide a home for wildlife and cooling shade
vital for fish and other aquatic creatures. The plant recovers rapidly after
wildfire, sending up hardy new sprouts from its roots. What's more, bits of
Arundo that break off and travel down creeks and streams can readily
start new infestations.

Despite the weed's long
history in the United States, there's very little published information about
its basic biology and ecology, according to David F. Spencer. He is with the
ARS team at Davis.

To help fill in the gap, Spencer and colleague Greg G.
Ksander, also at Davis, are gathering data needed for equations that can be
used to predict Arundo's growth at various stages of its life cycle
under various environmental conditions. Explains Spencer, "Some of
Arundo's life stages may be more susceptible than others to certain
control tactics, like herbicides or biological control. And environmental
conditions such as temperature are likely to influence growth and development,
but we don't have specific details."

As a starting point, Spencer and Ksander looked at the
effects of temperature and soil nitrogen levels on sprouting. "We want to
determine the environmental conditions that cue Arundo to produce new
sprouts from its rhizomes." Those thick, underground stems are critical to
Arundo's long-term persistence.

In tests of rhizome
sections and stem cuttings kept indoors for 12 weeks at 44.6 °F, 57.2
°F, or 68 °F, the researchers found that new shoots emerged and
survived at 57.2 °F and 68 °F and emerged sooner at the higher
temperature. At 44.6 °F, no shoots grew from rhizome sections; only a
single shoot sprouted from a stem cutting but soon died.

In a second experiment, the scientists varied the level of
the nitrate form of nitrogen applied to rhizome sections during weekly
watering. Notes Spencer, "Some studies done at other labs have indicated that
nitrate in the soil, which may fluctuate seasonally, stimulates some seeds to
germinate."

The researchers exposed rhizome sections to 46.4 °F or
60.8 °F for 14 weeks and applied concentrations of nitrate ranging from 0.3
to 6.0 milligrams per liter of water. "New shoots emerged at 60.8 °F but
not at 46.4 °F," reports Spencer. "Neither the number of shoots that
emerged nor the length of time it took for them to appear was influenced by the
amount of nitrate that we applied."

In an experiment with rhizomes planted outdoors at Davis,
the scientists found that shoots first appeared in late March, when the average
weekly temperature was 52.7 °F. New shoots continued to emerge until
November.

"With this new information, we can develop equations that
relate sprouting to temperature over time, or what's known as accumulated
degree-days," Spencer says. "Because nitrateat the levels we
applieddidn't stimulate sprouting, the equations won't have to include
nitrate fluctuations."

Fish and wildlife specialists, water district managers, and
other streamkeepers throughout the United States can use the information from
the equations. It will help them decide the best timing for whatever management
technique they choose to bring this aggressive weed under control.By
Marcia
Wood, Agricultural Research Service Information Staff.

This research is part of Crop Protection and Quarantine,
an ARS National Program (#304) described on the World Wide Web at
http://www.nps.ars.usda.gov.

As if giant reed
weren't enough of a problem, this rugged invader often grows interspersed with
another waterside menace, saltcedar, or Tamarix parviflora. These weeds
may leave off further inland, but then another unwelcome intruder, called
yellow starthistle, Centaurea solstitialis, often takes over.

"These
exotic species are thought to be the three most serious plant invaders in
riparian ecosystems and adjacent uplands in the West," says ARS ecologist
Raymond I. Carruthers. He is leader of the ARS Exotic and Invasive Weeds
Research Unit, based at the Western Regional Research Center in Albany,
California.

Funded
in part by a grant from the Initiative for Future Agriculture and Food Systems,
Carruthers co-manages a unique research project aimed at helping land managers
tackle all three problem weeds at once in what's known as an ecosystem-level
approach. At least three dozen federal, state, and private agencies,
universities, and organizations are working together to develop the best
biological control strategies for combating these weeds and restoring native
plants.

"People
have joined this team effort because they're convinced that biological control
has the ecological and economic potential to fight established invasive
species," says Carruthers.

Program
participants are sharing the work of evaluating the risks and effectiveness of
biological control agents such as weed-eating insects. They are also helping
develop innovative techniques to prevent the weeds from successfully
reinvading. And they're helping make sure that land managers have the newest
and best available information about successful weed-management strategies.

"Results
of this project," notes Carruthers, "may provide a model that people elsewhere
can use to get the upper hand with other groups of invasive plants."By
Kathryn Barry Stelljes, formerly with ARS.